1. Field
The disclosure relates to the machines and processes for powder-based additive manufacturing by sintering or melting grains of said powder using an energy beam such as electromagnetic radiation (for example a laser beam) or a beam of particles (for example an electron beam).
In particular, the disclosure relates to the architecture of the machine and to the means and processes for layering, that is to say for preparing, the bed of powder prior to sintering or to melting of said layer using the energy beam.
2. Description of Related Art
Document EP-1641580-B1 in particular discloses a layering device for sintering powders (metallic or ceramic) by laser. This device comprises a feed tray that allows the powder to be stored and to be delivered in a controlled quantity to a grooved roll capable, on the one hand, of transferring said quantity of powder onto and distributing it over the depositing tray during a first passage of the roll over the working zone and, on the other hand, of compacting the powder by a rolling movement of the roll during a second passage. The powder is then subjected to the laser beam. One disadvantage of this configuration is the size and the considerable cost of the feed tray. Another disadvantage is derived from the fact that the length of the working zone is limited by the useful perimeter of the roll.
Document WO-2011/007087-A2 discloses a layering device for melting powders by laser. This device comprises a feed tray that allows the powder to be stored and to be delivered in a controlled quantity to a scraper system capable of feeding the depositing tray and roll(s) capable of distributing said quantity of powder over and compacting it on the depositing tray. The powder is then subjected to the laser beam. One disadvantage of this configuration is the size and the considerable cost of the feed tray and also the necessary complexity of the machine on account of the large number of tools to be controlled (scraper, distribution and/or compacting roll(s), rams for the trays).
Document U.S.-2005/0263934-A1 discloses a layering device for sintering powders by laser. This device comprises feeding and metering means that allow the powder to be delivered in a controlled quantity in the vicinity of the working zone. Feeding takes place by gravity from a stock of powder situated above. A scraper makes it possible to adjust the thickness of a mass of powder, which is then subjected to a preheating operation. A rotary roll then makes it possible to transfer said quantity of preheated powder to and distribute it over the working zone. A quantity of powder may likewise be deposited on the cover of the carriage carrying the roll from one side of the working zone to the other and is thus only applied during the return of the roll. One disadvantage of this configuration is the risk of a part (even a very small part) of the powder being retained on the cover and subsequently falling into the working zone during the passage of the carriage above the bed of powder. This risk is not acceptable in the context of industrial use.
An additional problem that is common to the various proposals in the art is low overall productivity of the installation, since melting is interrupted during the layering phases and, conversely, layering cannot take place during melting phases.
Another problem that is common to the various proposals in the art is the difficulty and sometimes the impossibility of achieving a homogeneous thickness and density for the powder layer over the entire extent (length, width) of the working zone.